1. Field of the Invention
The present invention relates to a heat flow flux type differential scanning calorimeter.
2. Description of the Related Art
In the heat flow flux type differential scanning calorimeter (DSC), holders for a measurement sample and a reference substance are arranged in a heat sink through the intermediation of thermal resistances, and a temperature difference between the measurement sample and the reference substance is measured as a function of temperature. Between the heat sink and the holders, heat flows are generated through the thermal resistances, and a heat flow difference therebetween is proportional to the above-mentioned temperature difference. This temperature difference is then detected by using thermocouples or the like, and is therefore output as a DSC signal.
In the heat flux DSC described above, detection sensitivity (S/N ratio between baseline and noise) and resolution are two basic performance characteristics. The detection sensitivity is improved as the resistance value of the thermal resistance is larger. On the other hand, the resolution of the DSC is determined based on sharpness of a peak of a profile that is detected relative to a lapse of time or a change in rising/dropping temperature. The resolution is improved by increasing a response speed to obtain a profile having a sharper peak appearing on a DSC curve. The resolution (response speed) is improved by reducing the thermal resistances to increase a heat flow rate. In other words, the detection sensitivity and the resolution hold a trade-off relation, and therefore improvement in both the detection sensitivity and the resolution is demanded.
In view of the above, there is disclosed a technology in which a plurality of thermocouples are connected in series on a substrate through multiple connection and holders for a measurement sample and a reference substance are placed on the thermocouples (Japanese Patent Application Laid-open No. 2005-134397 (FIG. 2)). This technology is intended to enhance detection sensitivity by connecting the plurality of thermocouples in series to increase a thermoelectromotive force.
Further, there is disclosed a technology in which a platform 1 for a measurement sample and a platform 4 for a reference substance are connected to a common sensor body 6 through the intermediation of cylindrical tubes 2 and 5, respectively (U.S. Pat. No. 6,431,747 (FIG. 2)). The sensor body 6 is made of constantan to serve as one metal of a thermocouple, and the thermocouple is formed between the sensor body 6 and a lead wire 9 made of another metal, chromel, to thereby measure a temperature of the sample on the sample platform 1. Similarly, a temperature of the sample on the platform 4 for the reference substance is measured by a thermocouple formed between the sensor body 6 and a lead wire 11 made of chromel. The technology described in U.S. Pat. No. 6,431,747 (FIG. 2) is intended to improve the sensitivity by calibrating the sensor based on thermal resistance and heat capacity.
In the case of the technology described in Japanese Patent Application Laid-open No. 2005-134397 (FIG. 2), however, the plurality of thermocouple wires are connected in series while being insulated, and hence the thermal resistance serves as the substrate (MACOR: one kind of ceramics), which is arranged in a heat sink made of Ag and serving as a heat source, resulting in a large divergence of a coefficient of thermal expansion between the substrate and the heat sink. Accordingly, the contact state of the substrate and the heat sink changes at the time of scanning in a temperature range of approximately 900° C. at maximum, which may consequently cause deterioration of data reproducibility and noise.
In the technology described in Japanese Patent Application Laid-open No. 2005-134397 (FIG. 2), detected is a temperature difference between a reference temperature of an outer periphery of the ceramic substrate and a temperature of an inner periphery thereof, on which a sample container and a reference container being temperature measurement subjects are arranged. It is originally ideal if the reference temperature is set at a stable portion having as small a temperature fluctuation as possible, but in the method described in Japanese Patent Application Laid-open No. 2005-134397 (FIG. 2), when there occurs disturbance such as a slight temperature fluctuation of a gas flowing in the apparatus and of the heat sink or the above-mentioned change in contact state of the thermal resistance and the heat sink, the reference temperature itself fluctuates and as a result, there arises a problem of reduction in differential thermal detection accuracy.
In the case of the technology described in U.S. Pat. No. 6,431,747 (FIG. 2), on the other hand, the platforms 1 and 4, the cylindrical tubes 2 and 5, and the sensor body 6 are made of constantan, and the cylindrical tubes 2 and 5 function as the thermal resistances. At the same time, the platforms 1 and 4, the cylindrical tubes 2 and 5, and the sensor body as a whole are made of constantan, and serve as a negative terminal of a type E thermocouple, to thereby also function as a source of thermoelectromotive force for differential thermal detection and temperature detection.
In this case, at the time of scanning in a temperature range of approximately 900° C. at maximum, the constantan portion of each of the platforms 1 and 4 and the cylindrical tubes 2 and 5, in particular, the junction interface between the sensor body 6 and the heat sink may be distorted due to thermal deformation or the like, which may cause abnormality in electromotive force. This leads to abnormality in thermoelectromotive force for differential thermal detection and temperature detection, which may cause deterioration of data reproducibility and noise.
Further, the differential thermal detection is performed by using a pair of thermocouples, and hence there arises a problem that the electromotive force is fundamentally small and sensitivity cannot be increased.